One of the difficulties encountered in the realization of a timepiece of this type consists of assuring the fluid tightness thereof where the time setting stem traverses the case. In effect, it is known that fluid tight sealing on the surface of a hard material such as stone can only be mediocre.
For this reason there has already been proposed an assembly arrangement for the time setting stem which includes a tube radially driven into the base plate of the movement so as to be fluid tight with the base plate and traversed by the time setting stem. The latter receives at its outer extremity the crown which in turn is rendered fluid tight on the outer end of the tube by a packing fixed between an annular flange on the crown and the outer surface of the stem.
This arrangement has not proven satisfactory for several reasons.
Firstly, it necessitates the presence of the tube which must be manufactured and assembled, this increasing the price of fabrication of the timepiece.
However, if the case is fashioned at least partially of hard material, i.e. includes most frequently an outer caseband manufactured from this material (in order to render the case wear resistant), it is necessary to provide where the tube traverses this caseband, a clearance opening downwardly and extending to above the tube. This clearance is necessary to enable placing the movement provided with its tube into the case.
It is known that the machining of a hard material gives rise to serious problems since the risks of rupture of the workpiece in the course of being machined are very high. The clearance in question considerably weakens the workpiece at the place where it must be provided in a manner that said risks increase still further. Furthermore, when the timepiece is worn, the clearance may form a starting place for ruptures in case of shocks.
There has been furthermore proposed (U.S. Pat. No. 4,620,798), in a watch case including an outer caseband of hard material and an inner caseband of rigid but readily machinable material, to provide in the inner caseband a clearance for the crown, this clearance being closed on the outer side by the corresponding part of the outer caseband, but which opens downwardly in order to render the crown accessible. The stem fixed to the crown then traverses a radial hole pierced in the inner caseband in which sealing is assured by means of an annular packing placed in a groove machined in the stem. This packing is pressed against the wall of the radial hole.
This arrangement naturally guarantees a very satisfactory sealing since the packing acts on metallic surfaces, but it leads to a rather mediocre operability of the crown since the latter must be operated via the back face of the watch.
This invention provides a watch equipped with a mounting arrangement of the type described above which avoids these difficulties.